“Pains” are roughly classified by causes of diseases into nociceptive pain (so-called general “pain”) caused by a strong stimulus (nociceptive stimulus) that would result in damages to body tissues, and neuropathic pain, which is a disease pain resulting from an injury or malfunction of the central or peripheral nerve. This neuropathic pain causes, in addition to a spontaneous pain, a symptom such as a hyperalgesia that lowers the pain thresholds against the nociceptive stimulus and a severe pain (allodynia) caused by tactile stimulation that usually does not induce the pain. Once the morbid state is completed, it turns chronically whereby the outcome is very intractable.
At present, non-steroidal anti-inflammatory drugs (NSAIDs), non-narcotic analgesics, narcotic analgesics, and the like are used against general “pains,” so that therapeutic methods therefor have begun to be established. However, there are hardly any analgesics that can satisfy the neuropathic pains under the current situation.
As a result of intensive studies on the compounds that show effects on various pains, the present inventors have found that the cinnamic acid amide derivative of the present invention has excellent analgesic actions to not only a nociceptive pain model animal but also a neuropathic pain model animal. As cinnamic acid amide derivatives, Patent Publication 1 discloses a compound having antidepressant action and analgesic action. However, only the effects on nociceptive pains are evaluated, and actions on chronic pains such as neuropathic pains are not described at all.